1. Field of the Invention
The present invention relates generally to a method of heat transfer and a heat exchange device therefor, and more particularly to a vortex heat transfer method and a vortex heat exchange device therefor.
2. Description of the Art
Heat exchangers are devices that transfer heat between fluids of different temperatures. Heat exchangers are widely used in industries of all types, e.g., power generation, chemical processing, food, metallurgy, energy, aerospace and aeronautics, air-conditioning and refrigeration, automotive, and other types of manufacturing. Since such a wide range of industries use heat exchangers, various types of heat exchangers are available.
Traditionally, heat exchangers are designed and modified based on Newton's Law of Cooling: EQU Q=hA.DELTA.T (1)
where Q is the rate of heat transferred between two fluids, .DELTA.T is the average temperature difference between the hot and cold fluids, A is total surface area for heat transfer, and h is a constant called heat transfer coefficient. In reality, h is not a constant but is rather a complex parameter. The heat transfer coefficient h changes with the geometry and arrangement of the system, and the fluids and their characteristics within the system. While equation 1 is an over-simplification of the fundamental phenomena of heat convection, it does demonstrate that the rate of heat transferred is proportional to the heat transfer surface area, the average temperature difference between the two fluids, and the heat transfer coefficient.
The object of heat exchangers is to increase the rate of heat transferred between fluids. Equation 1 suggests that by increasing A, .DELTA.T, or h, in any combination, Q will increase. In actual applications, however, it is usually difficult to increase A greatly because of the size and costs of the heat exchanger is predefined by its application. It is also difficult to increase .DELTA.T because the average temperature differential must conform to the application conditions. Because of these restraints, most heat exchangers primarily rely on improvements in the heat transfer coefficient. Accordingly, heat exchangers have evolved from the double-pipe, to the tube-and-shell, the finned plate (cross-flow), the tube inserts, and to the recent impulse flow heat exchanger.
Since most design and operating variables of heat exchangers are lumped into the complex heat transfer coefficient, designers have less chance to pursue a comprehensive optimization of the performance of heat exchangers using the adjustable variables. Many of the measures taken so far tend to be straight forward but have had limited effect. For example, a large increase in the flow velocities of the hot and cold fluids can greatly increase h. However, the increase in flow velocity also increases the required pressure drops (or required pumping power to achieve the desired velocity) in the system. The increase in flow velocity shortens the residence time of hot and cold fluids which reduces the effect of improvement in Q.